Screening of Tropical Fruit Volatile Compounds Using Solid-Phase Microextraction (SPME) Fibers and Internally Cooled SPME Fiber EDUARDO CARASEK † AND JANUSZ PAWLISZYN* Department of Chemistry, University of Waterloo Waterloo, Ontario N2L 3G1, Canada In this study, the optimization and comparison of an internally cooled fiber [cold fiber with polydimethylsiloxane (PDMS) loading] and several commercial solid-phase microextraction (SPME) fibers for the extraction of volatile compounds from tropical fruits were performed. Automated headspace solid-phase microextraction (HS-SPME) using commercial fibers and an internally cooled SPME fiber device coupled to gas chromatography-mass spectrometry (GC-MS) was used to identify the volatile compounds of five tropical fruits. Pulps of yellow passion fruit (Passiflora edulis), cashew (Anacardium occidentale), tamarind (Tamarindus indica L.), acerola (Malphigia glabra L.), and guava (Psidium guajava L.) were sampled. The extraction conditions were optimized using two experimental designs (full factorial design and Doehlert matrix) to analyze the main and secondary effects. The volatile compounds tentatively identified included alcohols, esters, carbonyl compounds, and terpernes. It was found that the cold fiber was the most appropriate fiber for the purpose of extracting volatile compounds from the five fruit pulps studied. KEYWORDS: Fruits; volatile compounds; experimental design; solid-phase microextraction, cold fiber INTRODUCTION Aroma is one of the most important attributes that affects the consumption of fruit from the tropics and subtropics. Because these fruits are often inexpensive and extremely rich in vitamins, their popularity has increased, especially in Europe and the United States. In Brazil, tropical fruits are eaten fresh locally during the whole year and are exported to other countries normally in the form of frozen pulp (1). Acerola pulp is very juicy and cooling and possesses a fruity and sweet flavor, but the fruit is principally known for its amount of vitamin C. Yellow passion fruit possesses a floral, estery aroma with an exotic tropical sulfury note. Special nutrition interest has been given to cashew fruit because of its good characteristics for industrialization owing to its fleshy pulp, soft peel, lack of seeds, high sugar content, and strong exotic flavor. Tamarind fruit is high in sugar and minerals, with a pleasant acid taste and rich aroma. Varieties of guava fruit can differ widely in flavor and seediness. The better varieties are soft when ripe and creamy in texture with a rind that softens to be fully edible. The sweet, musky odor is pungent and penetrating. The seeds are numerous but small and, in good varieties, fully edible. The main volatile compounds identified in yellow passion fruit belong to the esters (2-4). Prior studies that used the solid- phase extraction technique to isolate the volatile compounds from the cashew fruit indicate that the most intense (and common) compounds identified in this fruit were methyl and ethyl esters (5). Phenylacetaldehyde and furfural are cited as the most common compounds of tamarind fruit (6, 7) while for the acerola the esters were predominant (8, 9). The aroma of guava is composed of a large number of ester and terpenoid compounds (10-14). Recently, for the purposes of determining fruit aromas, the solid-phase microextraction (SPME) technique has been applied as an alternative sample preparation strategy, to overcome the problems associated with conventional sampling methodologies, such as elevation costs, time-consumption, and the use of large volumes of organic solvents. In addition, the SPME procedure will more closely reflect the true flavor profile of the fruit pulp than those that might be generated by distillation and solvent extraction processes. Among the SPME fibers commercially available, those fibers that contain liquid (PDMS) and solid [carboxen (CAR) and/or divinylbenzene (DVB)] components have been chosen for the extraction of volatile fruit pulp com- pounds due to their high sensitivity (15-19). However, because a high desorption temperature is required, the formation of artifacts is often unavoidable with these coatings. Investigations of artifact formation during the analysis of volatile sulfur compounds (20) and volatile amines (21) in air by CAR/PDMS have been reported. Thus, the development of new fibers would allow for improved extraction efficiency and low desorption temperatures (20). Alternatively, the use of an absorbent coating (in place of an adsorbent coating), which requires a low desorption temperature, would also help to reduce the formation * To whom correspondence should be addressed. Fax: +1 519 746- 0435. E-mail: janusz@uwaterloo.ca. † On leave from Departamento de Quı ´mica, Universidade Federal de Santa Catarina, Floriano ´polis, SC, Brazil, 88040-900. 8688 J. Agric. Food Chem. 2006, 54, 8688-8696 10.1021/jf0613942 CCC: $33.50 © 2006 American Chemical Society Published on Web 10/03/2006